The invention relates to an electron-beam recording medium with a coating, applied to a substrate, which contains a phosphor and is sensitive to electron-beam radiation.
The electron beam-sensitive coating is also designated hereinafter as the "phosphor coating" or "storage coating" for the sake of simplicity.
A recording medium of the above-mentioned type is known from DE-OS No. 19 63 374. The phosphors mentioned herein are thallium-doped potassium iodide and manganese-doped potassium magnesium fluoride. When data is written with an electron beam, the phosphors luminesce; at the same time, defects are formed which extinguish the luminescence. These defects can be eliminated or healed by heating. This medium, therefore, is a recording medium for the reversible recording of data.
In the known recording medium the storage of data is based on the formation of areas of different degrees of radiation defects on the surface of the electron-luminescent phosphor, i.e. the thickness of the phosphor coating is to be selected in such a way that it is almost penetrated, but not quite by the electron beam which bombards the coating. Storage on the surface has the disadvantage that the stored information is sensitive to contact, weathering the other surface-damaging influences.
The use of phosphors based on halogenide crystals in electron beam recording media has the further disadvantage that these crystals are hygroscopic. This makes the production of phosphor-based recording media which is simple in principle somewhat more difficult, and care must be taken to ensure that the phosphors are protected against air humidity during subsequent use of the recording medium.
In addition, local defect concentration differences of the aforementioned type have a tendency to even out. This effect is presumably due to diffusion. The diffusion rate of the defects depends both on the concentration gradients of the defects in the crystals and on the temperature. It increases with both. The result of this is that there is a permanent tendency towards information loss. In the patent mentioned earlier, this effect which is particularly prominent at elevated temperature is intended after all as an erasure mechanism for the written information.
The intrinsic tendency of the phosphor type contained in the known recording medium to restore the chemical equilibrium by diffusion of accumulations of localized defects imposes a natural limit on the highest number of 0.fwdarw.1 items of information which can be written per unit surface. According to the above-mentioned patent, only 10.sup.7 bits of digital information are stored on a disc of 4.times.6 mm.sup.2.
DE-OS No. 30 32 611 describes organic rare earth metal salt type phosphors which are capable of emitting radiation when subjected to excitation by, among other things, electron bombardment and which are suitable, among other things, as photographic materials, picture-resolving materials or high-resolution materials, and as basic materials for the field of optoelectronics.